Neithan Tol Turambar

Rather than dig out the books, I will concede your point.
Many times in Tolkiens work we are left delicious moments to ponder. So, we must use our wits, and extrapolate. 'Inference', I believe.
Let's say that instead, Boromir had come across a band of orcs, who had with them an artifact, statue bust or somesuch, taken from the fallen city of Minas Ithil. Lets say, he found them not even on land named to the kingdom of Gondor, say, on the southern borders of Imladris? (sp?) Would he then have the right and duty as Captain of the White Tower to assault, kill, and take the statue bust? Even if the orcs were not in a position to directly theaten the security of Gondor?
I think to argue that a soldier of Gondor did not have clear directive to attack and destroy, taking posesson of any weapon that might, having been left behind, come into the posession of yet another enemy of Gondor, perhaps more dangerous that the first, Would be inane and vacuous.
Clearly, servents of the Steward of Gondor were bound to take action against what at the time, appeared to them, in all reasonable appearences, to be a clear and impending threat to the peace and safety of the Steward whom they serve, unless, some captain of greater rank be present, in which case, a soldier would be bound to defer to the ranking commander, and be subject to his discretion.
In the case of Boromir, in which I offered my opinion, Aragorn was that higher ranking officer. The evil power of the Ring blinded him to that truth in the pivotal moment of trial. And yet, at the moment of his curse, "Curse all halflings to death and darkness!" He tripped on a root and lay sprawling, as if his own curse had struck him down. Then suddenly he wept.

'Here do I swear fealty and service to Gondor, and the Lord and Steward of the realm...'

And if you still think my observation in the post about the Departure of Boromir is incorrect, then by golly, you must be right after all. I'll think more about it tomorrow my friend, for I don't know about you, but I'm on Pacific time.